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Not a Hyundai repair but I thought I'd share it anyway.

Had a customer with an alarm fault on a Mazda 2. The Alarm siren wasn't working.
No big deal I thought, I can just replace the factory siren with an aftermarket one. Luckily my missus drives the same car so I already knew the siren was in the boot/trunk. I'd have never thought to look in there otherwise, and with the siren not working I'd probably have never found it.

Anyway, I removed the boot trims to gain access to the siren and find that it has 3 wires on the connector rather than the 2 I was expecting. Probing the wires I found it had a constant 12V supply and constant ground, so an aftermarket siren wasn't going to work. It would just be sounding all the time. The third wire was some sort of digital data bus (LIN BUS I'm guessing)...see scope trace below. Since I had already removed the boot trims to get at the siren I decided to have a go at repairing it rather than have to fit all the trims then remove them again after I bought a replacement unit. I figured it was faulty and I wasn't going to make it any more faulty by having a go.

The siren was mounted inside a metal box which was kinda crimped together. I had to grind off the crimped sections of the box to get it open. So I remove the siren from it's metal box and find that the plastic case of the siren is a sealed enclosure. It looked like the two halves had been bonded together. So back to the grinder, fit a cutting disc and cut the plastic case open.

Inside the plastic case there are 3 components. A backup battery, a rather busy electronic circuit board and a Piezo sounder. As you can see in the photo below, there was no sign of obvious damage and I'm thinking something has blown on the circuit board and it's a complicated looking circuit that's way over my head. I give the board a good look over, checking for dry solder joints or anything obvious that I might be able to repair but nothing found. I'm just about to chuck the thing in the bin when I pick it up and the black wire comes off the sounder....RESULT! The wire was broken and just being held on with a blob of hot snot glue. I resoldered the wire and secured it with some Araldite. Plugged the 3 parts back together and connected it to the car harness for a quick test....WOW it works!

I glued the plastic case back together with the aforementioned Araldite and duck taped the metal case...who's gonna see it. Put the boot trims back on and retest...thankfully it's still working.

To be honest, it probably wasn't worth all the trouble because when I checked e'bay later I found you can buy a used siren for about £30. But I got a little sense of self satisfaction at finding the fault (even if it was by accident) and repairing it. With all the complex electronics on cars these days we don't often get to actually repair anything anymore.

Data Packets - Siren Data Bus with Alarm Armed


Had to grind these crimped tabs off to open the box


The car was a Mazda but the siren is a Ford Motor Co Part


Inside the siren. Sounder to the left, PCB, and backup battery to the right



It was a bit of a fluke...but I found the fault
 

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Cool! Loved the duck tape comment.

The difference between you and me is that I use duck tape where people can see it and I have to take my car to a mechanic for a repair like this.:laugh:
 

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Feels good to find the fault and work out a fix.
Quite enjoyed the write up
So, the charge for the fix was the same as replacement part and labor?
Or did you just charge for labor?

I remember one customer dropped their 13 inch B&W TV
The High voltage coil split. Glue the pieces back together and soldered wires
Worked like new. Only charged $15 dollar to fix.
At the time, a new 13 inch B&W TV would cost about $120 dollar.
 

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Discussion Starter #4
Quite enjoyed the write up
Thanks. I thought it was just worth showing how complex cars are getting these days when something as simple as an alarm siren has a networked computer built in.

avisitor said:
So, the charge for the fix was the same as replacement part and labor?
Or did you just charge for labor?
I didn't fit any parts so I just charged for my time.
 

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I have a Nissan Pulsar at the moment and it won't start. The codes are key read errors and another key diddn't fix it. There is a key reader module that is the suspect. $900 for a new one.
 

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Discussion Starter #6
There is a key reader module that is the suspect. $900 for a new one.
You'd need to be pretty confident in your diagnosis to be spending that sum of money.

I'm not that familiar with the technicalities of the NATS. Is a used one from another car not an option? On some systems the key reading module isn't a coded part and can be swapped between different cars without having to code anything.
 

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Isn't it marvelous that something that was so simple now has to be microprocessor controlled.
It's become a disposable world we live in. Look at the work Spark had to go through to get into the alarm box. It's a completely unserviceable part meant to be pulled, tossed and replaced. It's rather sad and wasteful.
 
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